As an example of the technique for obtaining a crosslinked polysaccharide gel, Eur. J. Pharm. Sci., 2002 March; 15(2): 139-48 describes an example in which chondroitin sulfate (hereinafter also referred to as “CS”) is crosslinked using diglycidyl ether as the crosslinking agent to form the gel. However, when such a crosslinking agent is used, crosslinking reaction occurs simultaneously with the reaction of chondroitin sulfate with the crosslinking agent, thus causing a problem of having difficulty in removing the unreacted crosslinking agent from the gel.
Accordingly, a technique has been developed for photo-crosslinking a photoreactive polysaccharide from which the crosslinking agent can be easily removed. For example, a technique is known in which a photoreactive glycosaminoglycan is obtained by binding a photoreactive crosslinking group in advance to glycosaminoglycan, the unreacted crosslinking agent is removed by purifying the photoreactive glycosaminoglycan, and then crosslinked-glycosaminoglycan is obtained by irradiating light (JP-A-6-73102). This literature describes a technique in which photoreactive chondroitin sulfate is obtained by binding a photoreactive crosslinking group to chondroitin sulfate, and the photoreactive chondroitin sulfate is dissolved in phosphate buffered saline and then crosslinked by irradiating ultraviolet ray under the state of solution using a mercury lamp to form the gel. However, when a gel of the crosslinked glycosaminoglycan is obtained by such a method, since crosslinking efficiency is poor by the crosslinking reaction under the state of the solution, it is necessary to irradiate light by preparing an aqueous solution containing a photoreactive glycosaminoglycan at a high concentration (10% or more), so that it cannot always be said that this is a method having good efficiency.
On the other hand, as a technique for efficiently crosslinking a photoreactive polysaccharide, for example, a technique is known in which photoreactive glycosaminoglycan prepared by binding a photoreactive crosslinking group to glycosaminoglycan is dissolved in an aqueous solvent, the resulting solution is frozen, and its crosslinking is carried out by irradiating light while keeping the frozen state (WO02/060971). By this method, a crosslinked glycosaminoglycan showing a spongy (porous) property having markedly superior water taking/discharging property is specifically obtained, and a crosslinked glycosaminoglycan showing a gel property is not obtained.